1. Field of the Invention
This invention relates generally to gas laser technology and more particularly to gas lasers whose discharge channels are formed in ceramic waveguide.
2. DESCRIPTION OF THE PRIOR ART
It is well known that discharges and small bore tubes using gases with homogeneously broadened laser transitions obtainable with mixtures of CO.sub.2, CO and N.sub.2 O permit operation at higher pressures. Pressure broadened optical gain lines are desirable inasmuch as they allow wider frequency tuning of a laser oscillator and they allow small amplitude variations when operating over a relatively wide range of frequencies near gain line center. It is also known that optimum pressures for laser action in wall dominated discharges are inversely proportional to the bore diameter. This makes it desirable to build laser tubes with samll bores or channels; however, in constructing such laser systems for optimum operation, certain problems are encountered. First of all, diffraction of the optical beam from the "guide" can lead to large diffractional losses unless curved mirrors are precisely positioned from the guide end to minimize these losses. Alternatively, flat mirrors which terminate the guide end reduce such diffraction losses to nearly zero while greatly improving mechanical stability by making the mirrors integral parts of the optical gain chamber. Secondly, small bores or channels introduce optical absorption losses and losses due to scattering from the wall surfaces. Thirdly, operation of small bore tubes reduces the wall surface area available for conductive wall cooling of the gaseous discharge. Noting that the optimum pressure is inversely proportional to the bore diameter while the area of the tube varies as the square of the wall diameter, the reduction of the heat transfer area makes heat removal a more serious problem, assuming that the electrical input power per unit length remains constant as the tubes are scaled to smaller diameters.
In U.S. Pat. No. 4,129,836, entitled "Frequency Stable Boron Nitride Channel Laser", which issued to the subject inventor on Dec. 12, 1978, and assigned to the present assignee, there is disclosed a ceramic waveguide gas laser wherein the waveguide consists of boron nitride and more particularly comprises two equal lengths of boron nitride contiguously placed together with one of the lengths including a longitudinal or lengthwise channel formed therein with the contiguous surface of the other length providing the fourth wall of a rectangular laser cavity together with flat mirrors secured to the opposite ends of the slabs. Two or more gas ports including electrode means are coupled to the channel through the boron nitride walls. Such a gas laser constructed from boron nitride which due to its high thermal conductivity and extremely low thermal expansivity, provides an improvement in frequency stability over heretofore known apparatus.
Efforts to modulate laser beams and more particularly to gas lasers, is also well knwon. In U.S. Pat. No. 3,806,834, for example, there is disclosed the concept of Stark effect modulation of CO.sub.2 lasers with deuterated ammonia (NH.sub.2 D). As disclosed therein, a modulating field can be superimposed on a DC bias voltage to achieve amplitude modulation of the laser beam.
Currently, gas lasers performing interrelated functions operate independently. For example, a local oscillator CW laser is separately constructed from a pulsed laser. This requires continuous sensing of the frequency difference of the two lasers and correction for frequency drifting by using a feedback circuit which makes incremental cavity length changes by applying a voltage to piezoelectric crystals or bimorphs. Additionally, each laser requires a separate set of optics. The independent thermal and mechanical motion of the laser cavities and gratings causes a continuous random drifting of the two laser frequencies with respect to one another.